For example, U.S. Pat. No. 5,987,174 discloses a road monitoring apparatus by an image processing for judging changes of the intensity and color of the road immediately before its own vehicle to enable to separate a traffic lane from the road by the intensity and color, thereby enabling to certainly recognize the traffic lane. Specifically, the road monitoring apparatus includes a camera A to take a color image of the front view in a traveling direction of the vehicle; a display unit B to display the processing result of the image data taken by the camera A while superimposing it on the original image data; an extraction processing circuit to extract pixels satisfying a predetermined extraction color condition from a screen by the image data; a color sampling circuit to sample color data from the extracted pixels; an extraction condition determining unit for determining an extraction condition based on the sampled color data. The road monitoring apparatus recognizes the traffic lane based on the extracted pixels, and further judges a lighting condition of the traveling road based on the color data sampled by the extraction condition-determining unit. According to the judgment result, the iris mechanism and the color conversion gain are controlled. However, this publication does not disclose a point that road markings such as a crosswalk and a stop line are recognized. In addition, even if the road marking is individually recognized by the technique described on this publication, the misrecognition may frequently occur, because a lot of road markings have a simple shape.
Thus, the road marking may individually be recognized by the conventional technique. However, there are problems in which the misrecognition may frequently occur or a time-consuming processing is necessary in order to decrease the misrecognition. However, because the vehicle is running, when it takes too much time to process one frame, the difference with a frame to be processed next becomes large. This causes further misrecognition and/or leakage of recognition. In addition, almost all the applications using the recognition of the road marking require a real-time processing.